The two chatted on Facebook and commenced a sexual relationship when she was 15.
The court heard the man supplied methamphetamine to the teen, but the role of grooming in the relationship was contested.
"Of course there is grooming in this case. There's the presence of drugs in initial contact," Crown prosecutor David Wiseman said.
"There has been significant harm to her. She speaks of the effects the drugs alone have had on her life," he added.
Judge Aitken said there was minimal grooming compared to some other local cases, where victims were supplied with cellphones and encouraged to skip school.
Defence counsel Andrew Speed said his client pleaded guilty in order to save the girl from giving evidence at trial.
"She said she didn't believe she was able to get pregnant, but I totally accept the pregnancy was an aggravating feature," Speed added.
The relationship ended soon after the teenager fell pregnant.
The court heard a paternity test proved the drug dealer was the father.
The sexual predator was arrested on indecency charges in May last year and granted bail four months later.
"You have no sense of community and no cultural engagement."
But Judge Aitken also said the man remained a risk to the young mother.
The dealer was also sentenced for supplying meth worth $700, and offering to supply 1812ml of the nervous system depressant known as Fantasy or GHB for $9000.
He was sentenced to four years and nine months in jail.
Judge Aitken said the 43-year was slowly developing some insights about why his offending was wrong.
"He certainly believed this was love. He's starting to rethink that."
• Phone the police on 111 or ask neighbours of friends to ring for you. • Run outside and head for where there are other people. • Scream for help so that your neighbours can hear you. • Take the children with you. • Don't stop to get anything else. • If you are being abused, remember it's not your fault. Violence is never okay
Where to go for help or more information:
• Shine, free national helpline 9am- 11pm every day - 0508 744 633 www.2shine.org.nz • Women's Refuge: Free national crisis line operates 24/7 - 0800 refuge or 0800 733 843 www.womensrefuge.org.nz • Shakti: Providing specialist cultural services for African, Asian and middle eastern women and their children. Crisis line 24/7 0800 742 584 • It's Not Ok: Information line 0800 456 450 www.areyouok.org.nz